A structure has been disclosed (see Patent Reference 1) in which the interior of an airbag for side impacts is partitioned into an upper chamber and a lower chamber by a seam, a communication portion that communicates between the upper chamber and the lower chamber is formed between the seam and a rear edge of the airbag, a tubular check valve is provided at the communication portion, a gas generator is disposed in the check valve, and an outflow of gas from the lower chamber to the upper chamber is impeded by the check valve. Thus, even if the body of a vehicle occupant strikes the lower chamber, gas pressure in the lower chamber is maintained at a high pressure.                Patent Reference 1: Japanese Patent Application Laid-Open (JP-A) No. 2004-256017        